1. Field of the Invention
The invention relates to a data transfer switch, more particularly to a data transfer switch which is relatively simple in construction, which is relatively small and which can be used to connect selectively a plurality of computer peripheral equipments to a computer system.
2. Description of the Related Art
Data transfer switches are used to connect a plurality of computer peripheral equipments to a single computer system.
Referring to FIG. 1, a first example of a conventional data transfer switch (1) is shown to comprise a printed circuit board (11), three connectors (12, 13, 14) which are mounted on the printed circuit board (11) and two sets of key-operated switches (15, 16). Each of the key-operated switch sets (15, 16) includes three switch units [(151-153), (161-163)] and a key body (154, 164). A spring assembly [(155-157), (165-167)] is provided between the key body (154, 164) and each of the switch units [(151-153), (161-163)]. The spring assemblies [(155-157), (165-167)] permit a previously pressed one of the key bodies (154, 164) to revert to an unpressed state when the other one of the key bodies (154, 164) is pressed.
When the key body (154) is pressed, the switch units (151-153) are activated so as to connect electrically the connectors (12, 13). Accordingly, when the key body (164) is pressed, the switch units (161-163) are activated so as to connect electrically the connectors (13, 14). The connector (13) therefore serves as a common connector. The key bodies (154, 164) are operated so as to transfer data from a selected one of the connectors (12, 14) to the common connector (13) or so as to transfer data from the common connector (13) to a selected one of the connectors (12, 14).
The main drawbacks of the conventional data transfer switch (1) are as follows:
1. The size of the data transfer switch (1) is relatively large.
2. The circuitry of the data transfer switch (1) is relatively complicated.
3. The data transfer switch (1) can be used to connect selectively only two connectors (12, 14) to a common connector (13).
Referring to FIG. 2, a second example of a conventional data transfer switch (2) is shown to be substantially similar in construction to the data transfer switch (1). The main difference between the two examples is that the data transfer switch (2) incorporates a two-position select switch (21). The key body (211) of the select switch (21) is operated once in order to connect electrically the connectors (22, 23) and is operated for a second time in order to connect electrically the connectors (23, 24). Note that the size of the data transfer switch (2) is smaller than that of the data transfer switch (1) because a different switching arrangement is employed. However, the circuitry of the data transfer switch (2) is still relatively complicated. Furthermore, the data transfer switch (2) can be used to connect selectively only two connectors (22, 24) to the common connector (23).
A more complicated circuitry and switch arrangement is usually required in order to enable a data transfer switch to connect selectively more than two connectors to a common connector. Referring to FIG. 3, a third example of a conventional data transfer switch (3) includes a four-position switch set (31), five connectors (32-36) and five ribbon cables (321-326) respectively connected to the connectors (32-36). The switch set (31) is mounted on a printed circuit board (311) and includes five switch units (312-316). Each of the switch units (312-316) has a control lever which extends through a respective one of five openings (3121-3161) that are formed in a switch actuator (317). The switch actuator (317) has a central portion that is provided with a rack (37). A rotary knob (39) has an axle (391) which is provided with a pinion (38) that engages the rack (37).
Rotation of the rotary knob (39) can cause corresponding rotation of the pinion (38), thereby moving the rack (37) so as to result in left or right movement of the switch actuator (317). Movement of the switch actuator (317) causes corresponding movement of the control levers of the switch units (312-316). Simultaneous operation of the switch units (312-316) causes the connection of a selected one of the connectors (32, 33, 35, 36) with the common connector (34) via the ribbon cables (321-361), thereby permitting the transfer of data from the selected one of the connectors (32, 33, 35, 36) to the common connector (34) or the transfer of data from the common connector (34) to the selected one of the connectors (32, 33, 35, 36).
Note that although the data transfer switch (3) permits the selective connection of four connectors (32, 33, 35, 36) to the common connector (34), the data transfer switch (3) has a more complicated circuitry and has a relatively large size.
Another example of a conventional data transfer switch which permits the selective connection of four connectors to a common connector is shown in FIG. 4. The data transfer switch (4) includes a plurality of linking assemblies (40) which serve as the main portion of the data transfer switch (4). Each of the linking assemblies (40) includes a pair of annular linking pieces (41, 42) and a rotary piece (43) provided between the linking pieces (41, 42). The linking piece (41) has three angularly spaced contact terminals provided on the outer periphery thereof and connected to the common connector (not shown). The linking piece (41) further has three inwardly projecting sectoral electrical contacts (411) which are connected electrically to a respective one of the contact terminals of the linking piece (41). The linking piece (42) has twelve angularly spaced contact terminals provided on the outer periphery thereof and alternately connected to four connectors (not shown). The linking piece (42) further has twelve inwardly projecting sectoral electrical contacts (421) which are connected electrically to a respective one of the contact terminals of the linking piece (42). The rotary piece (43) is formed with twelve radially extending slits (44). Three conductive spring pieces (45) are respectively provided in three of the slits (44) such that the spring pieces (45) are angularly and equally spaced on the rotary piece (43). A rotary knob (46) is operated so as to rotate the rotary piece (43), thereby causing the spring pieces (45) to connect the three electrical contacts (411) with a selected three of the electrical contacts (421).
Cables are soldered onto the contact terminals of the linking pieces (41, 42) and are used to connect the latter to the corresponding connectors. If 25-pin connectors are in use, nine linking assemblies (40) must be provided in order to permit the selective connection of four connectors to a common connector.
The data transfer switch (4) has several drawbacks. Note that the construction of the data transfer switch (4) is relatively complicated because of the large number of cables which is required. The data transfer switch (4) is difficult to assemble because each of the cables has to be connected to one of the contact terminals of the linking pieces (41, 42) and to one of the connectors. Improper connection of the cables can result in data loss. Furthermore, the cables can introduce a relatively large impedance into the system and can cause the generation of heat when the data transfer switch (4) is in use, thereby increasing the possibility of data loss.
Still another example of a conventional data transfer switch is shown in FIG. 5. The data transfer switch (5) is substantially similar to the data transfer switch (4), except that the cables of the latter are replaced by a printed circuit board. Although the data transfer switches (4, 5) permit the selective connection of more than two connectors to a common connector, the data transfer switches (4, 5) are relatively complicated in construction because of the large number of electrical contacts which is required (typically a multiple of the number of connectors that are available). The data transfer switches (4, 5) are thus difficult to manufacture. Furthermore, because of the complexity of the data transfer switches (4, 5), it would be difficult to troubleshoot the same in order to find the cause of a malfunction.